Field of the Invention
The present invention relates to a method and to cleaning system for cleaning the process gas in soldering installations and solder suction systems.
Background Information
For soldering in soldering installations, such as reflow soldering installations, usually fluxes are used which enable the metallic solder and the parts to be soldered to form a solid metallic connection. During heating, the flux reduces the surfaces of the faces to be joined and of the solder and, at the same time, prevents a renewed formation of oxides by forming a liquid protective layer. Another effect is the reduction of the surface tension of the liquid solder. Fluxes vary with regard to their composition, wherein the same depends on the type of the parts to be soldered. For electronics, often the organic substance colophony is used, which does not leave any corrosive residues during soldering and has a reducing effect during heating.
Depositions in the soldering installation are one problem which occurs with soldering installations. A large part of these condensed depositions, which develop during the soldering process, results from the high-molecular compounds which are present in the flux (e.g. colophony) Another part of the soldering fumes includes, to a large extent, gaseous components of the printed circuit board substrate and of the solder resist. When using colophony as a flux, the abietic acid included, in the colophony often constitutes a good part of the above-mentioned depositions.
With the soldering installations from the state of the art, usually, in the soldering process, a combination of a filter and a heat exchanger is used for cleaning the process gas, wherein, with some soldering installations, only process gas filters or only heat exchangers are used. By means of the process gas filter, high-molecular compounds are partly filtered out of the process gas physically. As a filter material, typically materials with a very large specific surface, such as polyester fleece, granulate or the like, are used here. The process gas that has been pre-cleaned in this way can subsequently be conducted past a number of heat exchangers, such that the low-molecular condensate components can condense at the cooler surface of the heat exchangers. With some soldering installations, the process gas is conducted past a heating source over a defined course and is heated to a temperature of more than 500° C. In the course of this, high-molecular condensate compounds are partly cracked and new low-molecular compounds develop, which can be filtered more effectively.
The problem with the soldering installations and solder suction systems known from the state of the art consists in the fact that the above-mentioned, methods for cleaning the process gas are insufficient and that undesired depositions of high-molecular compounds in the soldering installation occur again and again. With 80 percent of all soldering installations, the condensed depositions result from the colophony used in the flux. With other fluxes, these problems are also caused by high-molecular compounds.